I think the person that added up the cost of the pieces was simply trying to make the units be equivalent. They were assuming the supplied blade is junk and would need to be upgraded. The Scheppach as sold by McFeeleys & Grainger came with 25" rails so it needed the connectors and clamps to cut across a 48" sheet of plywood. Actually, that length would do a very poor job of that since you really need most of the 55" rail that comes with the Festool, Makita, and Dewalt to do a good job of cutting 48" plywood. Looks like you can get a 55" rail for the Grizzly so that is a big plus for Grizzly. Looks like the Grizzly comes with a finer blade but who knows how well it cuts.
Unfortunately, the rail and clamp kit look like they may work differently than the others. According to the Grizzly catalog, it looks like the clamps go on the top of the rails which would cause several problems. I can't see how you would make that work well at the start of the cut or let the rail be used on lumber much shorter than the rail. Interesting thing is that the rails and clamps look like a copy of the others so you would think that they would slide inside the track and stay out of the way like the others.
My European tool dealer friend says the kindest reviews of the cheap track saws say that they are "good for the price", not actually good. I think the best less expensive alternative is the Makita or Dewalt when they are periodically put on sale really cheap. The Makita kit, with Tanos case and 55" rail, was $309 at one local tool dealer a few months ago. The Makita is darn close to the Festool in function. The biggest negatives are no offside splinter guard, cutting the splinter guard on the rail when angled, and short non-detachable power cord.